1. Field of the Invention
The present invention relates to a lens barrel or a camera having a shutter which is used for the exposure control of the camera, and which particularly constitutes a mechanism for changing the fully-open aperture value according to a change in the focal length.
2. Description of the Related Art
Some of the so-called compact cameras wherein a photographing lens group is built in integrally with the camera body, are generally known as xe2x80x9czoom camerasxe2x80x9d, or cameras having a so-called zoom lens, which cameras allow photographing at an arbitrary photographing visual angle by varying the photographing visual angle. These zoom cameras have a zoom lens barrel capable of being set from the non-photographing position (collapsed state) to the xe2x80x9ctele positionxe2x80x9d, that is, the position where the focal length is the maximum, by moving back and forth the photographing lens group in the optical axis direction. Usually, once the power supply of the camera body has been turned on, the camera comes into a ready state for photographing, and photographing can be performed between the xe2x80x9cwide positionxe2x80x9d, that is, the position where the focal length is the minimum, and the above-mentioned xe2x80x9ctele positionxe2x80x9d.
Some zoom cameras have an aperture changeover mechanism and a shutter opening/closing mechanism which adjust the light amount when photographing. Also, as known in the art, there is a lens shutter mechanism which can serve both as an aperture changeover mechanism and a shutter opening/closing mechanism. In this type of zoom camera having a lens shutter mechanism, the shutter diameter is adjusted so that a desired photograph can be taken by changing the diameter of the lens shutter (aperture) corresponding to the brightness when photographing. As disclosed in Japanese Patent Laid-Open Nos. 2-254428 and 2-254431, a lens shutter mechanism which changes the fully-open aperture diameter (hereinafter, referred to as a xe2x80x9cfully-open aperture valuexe2x80x9d) of a lens shutter according to the focal length of a photographing lens, is also known in the art.
On the other hand, with a view to achieving miniaturization and cost reduction of cameras, there are step-type cameras among these zoom cameras. These cameras perform stepwise zooming both during the extension and the withdrawal of a lens barrel, and simultaneously perform focusing during either the extension or withdrawal of the lens barrel during the above-described zooming.
As in a camera proposed in Japanese Patent Laid-Open No. 9-211554, some of these step-type cameras are arranged so that a photographing optical system and a viewfinder optical system are interlocked with each other when the photographing optical system performs zooming, and that this interlocking between the photographing optical system and the viewfinder optical system is disconnected when the photographing optical system performs focusing.
Here, operations of this camera will be described with reference to FIG. 1. FIG. 1 is an operational view of a lens barrel (photographing lens group). When a photographer indicates a desired zoom position after turning on the power supply of the camera body, the lens barrel extends the photographing lens in the optical axis direction by rotating a zoom ring provided in the camera. Here, when the photographer sets a zoom position to the zoom position P1, the lens barrel once extends in the optical axis direction as indicated by the arrow (1), and then withdraws up to the photographing standby position with respect to the zoom position P1. These extension and withdrawal operations of the lens barrel are operations for moving only the viewfinder optical system in the optical axis direction to correct the visual field ratio of the viewfinder at the zoom position P1. In other words, the photographing optical system is interlocked with the viewfinder optical system while the lens barrel extends, but the interlocking thereof with the viewfinder optical system is disconnected while the lens barrel withdraws. As a result, only the viewfinder optical system can be moved in the optical axis direction. This allows the visual field ratio of the viewfinder to be set to an appropriate value. This series of camera operations are operations necessary for achieving a matching state between the visual field of the viewfinder and the photographing optical system of the camera. In addition, this camera action of preventing the lens from moving exclusively in the invariably fixed direction, serves the purpose of eliminating backlash in the gears.
When photographing is conducted at the zoom position P1, the lens barrel performs the operation indicted by the arrow (3). Specifically, by extending the lens barrel based on a subject distance, the camera moves the photographing lens group in the optical axis direction to perform focusing, and after performing an exposure operation by the opening/closing operation of a shutter mechanism, withdraws the lens barrel up to the photographing standby position with respect to the zoom position P1.
The operation of the lens barrel as indicated by arrow (3) is such that the lens barrel extends up to a position in close proximity to the focus point of the lens. However, since the extension amount of the lens barrel varies depending on the subject distance, the operation of the lens barrel is not limited to the operation indicated by the arrow (3).
When photographing is conducted at a zoom position P2 which has a focal length larger than that of the zoom position P1, the lens barrel performs the operation indicated by the arrow (4), as in the case of the zoom position P1.
As described above, in a zoom camera having a lens shutter mechanism, it is necessary to change the fully-open aperture value corresponding to the change in the focal length of the camera, and consequently, the change in the extension amount of the photographing lens in the optical axis direction, as set forth in Japanese Patent Laid-Open No. 2-254428. Herein, if the fully-open aperture value of the lens shutter changes during the focusing of the camera, this will make the exposure control of the camera significantly difficult, and therefore, the fully-open aperture value of the lens shutter is required to be constant during focusing. The changeover of the fully-open aperture value, therefore, must be performed except when focusing is conducted.
The foregoing will be elucidated with reference to FIG. 1. When it is necessary to change the fully-open aperture value of the lens shutter between the zoom positions P1 and P2, the changeover of the fully-open aperture value must be performed except when focusing is conducted, as described above. Therefore, the fully-open aperture value changeover region of the lens shutter mechanism is the region (7) in FIG. 1.
As in the shutter device disclosed in Japanese Patent Laid-Open No. 8-62668 to the same assignee as this application, a mechanism for changing over the fully-open aperture value by driving a cam pin engaged with a cam provided in a lens barrel, is known in the art as a lens shutter mechanism. When such a lens shutter mechanism is provided in a step-zoom type camera, it is necessary to drive a cam pin within the fully-open aperture value changeable region (7).
However, when attempting to perform photographing at many zoom positions or when attempting to minimize the rotational angle of the lens barrel so as to quicken the zooming action of the lens barrel, the range (7), which is the fully-open aperture value changeover region, necessarily must be made small. In the case of a camera which uses the above-described lens shutter mechanism, which changes the fully-open aperture value of the lens shutter by cam drive, it is necessary for the cam provided within the lens barrel to perform a large motion over a small rotational angle. This makes a steep cam lift rise of the drive cam within the lens barrel an inevitable consequence.
On the other hand, since there is a limit to which the amount of the cam can be varied, the limit of the lift amount of the cam formed within the lens barrel is inevitably determined, in order to stably perform cam drive. Once the limit to the cam lift amount has been determined, it is impossible to make the range of the fully-open aperture value changeover region (7) smaller than the limit value of the cam lift amount. There are limits, therefore, to enabling photographing at many zoom positions and to reducing the rotational angle of the lens barrel so as to quicken the zooming action of the lens barrel.
Accordingly, it is an object of the present invention to provide a lens barrel or a camera which enables photographing at many zoom positions, and allows the rotational angle of the lens barrel to be minimized, so as to quicken the zooming action of the lens barrel without imparing the smooth zooming and focusing of photographing lenses.
In order to achieve the above-described object, the present invention provides a lens barrel which comprises a variable power lens unit; an aperture-variable light-amount adjusting unit which has an adjusting member for adjusting the fully open state of the aperture; a variable power lens control mechanism for shifting the variable power lens unit from a first variable power position to a second variable power position, where the variable power lens control mechanism moves the variable power lens unit beyond the second variable power position, then the variable power lens control mechanism returns the variable power lens toward the second variable power position, and the variable power lens control mechanism stops the variable power lens at the second variable power position; and a cam member having a cam portion with which the adjusting member is engaged, and moving relative to the light-amount adjusting unit in operative association with the control action of the variable power lens control mechanism. Herein, the cam portion has a cam shape that drives the adjusting member while the variable power lens unit is moved at least beyond the second variable power position, but does not drive the adjusting member while the variable power lens unit is returned toward the second variable power position.
Preferably, the cam member moves in the optical axis direction of the variable power lens unit in operative association with the control action.
It is preferable that, when the variable power lens control mechanism shifts the variable power lens from the second variable power position to the first variable power position, the variable power lens control mechanism stop the variable power lens without moving the variable power lens beyond the first variable power position.
Preferably, the cam portion has a cam shape that drives the adjusting member when shifting the adjusting member from the second variable power position to the first variable power position.
It is preferable that the variable power lens control mechanism has a cam ring formed in a manner such that variable power cam portions which drive the variable power lens unit for scaling and focus cam portions which drive the variable power lens unit for focusing during extension of the variable power cam portion, are arranged in an alternating sequence.
Preferably, the cam portion has a cam shape that does not drive the adjusting member when the variable power lens unit moves on the focus cam portion for focusing.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.